An organic light emitting diode display module (AMOLED) is one of the hotspots within the field of flat panel display device researches. Compared to a liquid crystal display module, the organic light emitting diode display module has advantages such as low power consumption, a low production cost, self-luminous and wide viewing angle and fast response. At present, the organic light emitting diode display module has begun to replace conventional liquid crystal display module in the display area such as mobile phones, tablets and digital camera. Pixel driving circuit design is the core technology of the organic light emitting diode display module and has important research significance.
The organic light emitting diode display module can be classified into two types based on driving mode: a passive matrix organic light emitting diode (PMOLED) display module and an active matrix organic light emitting diode (AMOLED) display module, namely a direct addressing and a thin film transistor (TFT) matrix addressing. The active matrix organic light emitting diode display module, which has pixels arranged in an array form and high luminous efficacy, is of an active display type and commonly used as large-size high-definition display device. Unlike the liquid crystal display module using stable voltage to control brightness, the active matrix organic light emitting diode display module is driven by the current and need the stable current to control the light emitting thereof. Due to process technology and modular member deterioration and other reasons, the threshold voltage (Vth) of driving transistors of each pixel drifts, so that the current flowing through each pixel varies as the threshold voltage, thereby leading to the uneven display luminance. Meanwhile, IR-drop, caused by resistance of power supply lines connecting various pixels on the panel and the electric charges consumed by various pixels when emitting light, can also arouse the display unevenness, so that the pixels in proximity to the display pixel drive module are brighter while those away from the display pixel drive module are darker (that is, the pixels are getting dark with the distant from the display pixel drive module), thereby affecting the display effect of the entire image. Therefore, there is a need for the pixel driving circuit being capable of compensating the threshold voltage drift of the driving transistor and IR-drop of the supply power.